<head>
    <style>
        div
        {
            width:50px;
            height:50px;
            background:red;
            position:relative;
            animation:myfirst 5s infinite;
            animation-direction:alternate;
        }

        @keyframes myfirst
        {
            0%   {background:red; left:0px; top:0px;}
            25%  {background:yellow; left:200px; top:0px;}
            50%  {background:blue; left:200px; top:200px;}
            75%  {background:green; left:0px; top:200px;}
            100% {background:red; left:0px; top:0px;}
        }

        @-moz-keyframes myfirst /* Firefox */
        {
            0%   {background:red; left:0px; top:0px;}
            25%  {background:yellow; left:200px; top:0px;}
            50%  {background:blue; left:200px; top:200px;}
            75%  {background:green; left:0px; top:200px;}
            100% {background:red; left:0px; top:0px;}
        }

        @-webkit-keyframes myfirst /* Safari and Chrome */
        {
            0%   {background:red; left:0px; top:0px;}
            25%  {background:yellow; left:200px; top:0px;}
            50%  {background:blue; left:200px; top:200px;}
            75%  {background:green; left:0px; top:200px;}
            100% {background:red; left:0px; top:0px;}
        }

        @-o-keyframes myfirst /* Opera */
        {
            0%   {background:red; left:0px; top:0px;}
            25%  {background:yellow; left:200px; top:0px;}
            50%  {background:blue; left:200px; top:200px;}
            75%  {background:green; left:0px; top:200px;}
            100% {background:red; left:0px; top:0px;}
        }
    </style>
</head>
<body>

<p><b>注释：</b>本例在 Internet Explorer 中无效。</p>

<div></div></body>